With the recent findings that many juvenile-onset type diabetic (JOD) patients have circulating autoantibodies to pancreatic islet cells (ICA), there is increased interest in the possible use of such antibodies for clarification and understanding of the disease. Most of the studies concerning the humoral autoimmune response in JOD patients have been directed toward cytoplasmic islet cell antibodies. Less information is available regarding circulating cell surface islet cell antibodies (csICA) and the possible relationship of csICA to cytoplasmic ICA. Also, the identity and cellular location of islet cell antigen(s) to which ICA are directed is presently unknown. Since a major obstacle in these studies is the low antibody titres often found in these diabetic patients, we plan to develop methods for the isolation and concentration of csICA. Purified preparations of csICA will be used to test antibody specificity to organ, islet cell type, and cellular location. Experiments are described to test csICA for biological effects on islet cell functional response to secretagogue stimulation of hormone production and complement-mediated cytotoxicity. The possible biological effects of csICA will be investigated with isolated pancreatic islets, superfused islets and perfused pancreas as well as in vivo. The islet cell antigen(s) to which csICA is directed will be identified and isolated by immunoaffinity, immunoprecipitation, and subcellular and protein fractionation methods employing csICA as a specific reagent to detect putative antigen(s). Circulating immune complexes will be purified from diabetic patient sera by C1q or polyethylene glycolprecipitation and analyzed for the presence of islet cell antigen(s) and ICA. The relationship of csICA, cytoplasmic ICA, and HL-A type in diabetic patients will be investigated. We also plan to use secretagogue affinity chromatography and other protein fractionation procedures to identify and isolate cell components involved in secretagogue stimulation of hormone production.